Over the years there have been a multitude of systems for the detection of motion within a given zone or field of view. These systems include optical, ultrasonic, electromagnetic, electrostatic, microwave and passive infrared sensors. The passive infrared sensors may be of a type that include a pyroelectric component of a nature which exhibits an electrical voltage or a change of electrical resistance in response to infrared radiation which is radiated by an object, for example, a human body. Circuits in the sensor detect this change and respond by transmitting an actuating signal to one or more electrically controlled devices that are to be turned on when the object is in a zone monitored by the sensor. Such sensors may also include means for intercepting infrared that arrives from different directions and for concentrating the infrared at the location of the pyroelectric component. Typical of such detection systems is that shown in the Jacob Fraden U.S. Pat. No. 4,450,351 ('351) which describes an optical system for motion discontinuance detection in an optical field of view that has the ability to turn lights off in a room. The system produces an output signal change upon the discontinuance of motion within the field of view and not by the presence of motion within the field of view.
The Galvin et al U.S. Pat. No. 4,636,774 ('774) is directed to a motion detector together with associated A C switching circuitry which form a lighting control system which turns on room lights when the room is occupied and extinguishes the lights when the room is unoccupied. The '774 invention is specifically directed to a dual sensitivity motion detector which requires a substantial initial motion disturbance to turn on the lights, but once the lights are turned on the motion detector becomes highly sensitive to any motion in the room thereby keeping the lights on.
The Pfister et al U.S. Pat. No. 4,746,910 ('910) discloses a passive infrared intrusion detector which employs correlation analysis. The '910 invention employs a pair of sensors wherein signals obtained from a first sensor are indicative of motion detected in a region. These signals are continuously compared in a correlator with reference to set signals stored in a read-only memory and/or with actual signals obtained from a second sensor monitoring the region.
The W. Lee U.S. Pat. No. 5,066,855 is directed to the idea of motion monitoring two fields of view by means of a single sensor and an optical device.
The Hershkovitz et al U.S. Pat. No. 5,077,549 is directed to an integrating passive infrared intrusion detector where a signal responsive to infrared radiation received from optically divided zones of an area to be monitored is integrated to produce an integral sum to generate an alarm indication.
The A. L. Hermans U.S. Pat. No. 5,221,919 is directed to a room occupancy sensor of a standard pyrotechnic type which receives infrared energy from parties entering a room by means of a novel dome shaped collection of fresnel lenses that focus the infrared energy on a sensor.
The Ichikawa U.S. Pat. No. 5,153,560 ('560) is directed to apparatus for detecting presence of a person inside a room having a door. The apparatus includes a pyroelectric infrared sensor and a piezoelectric air pressure sensor. The infrared sensor detects movement of a person and produces a signal indicating movement. The air pressure sensor detects opening and closing of the door and produces a signal indicating the opening and closing of the door. A logic device is connected between the-outputs; of the two sensors. When the signal indicating the movement is applied to the logic device later than the signal indicating the opening and closing of the door, the logic device produces a signal indicating the entry of a person. When the signal indicating the opening and closing of the door is applied to the logic device later than the signal indicating the movement of a person the logic device produces a signal indicating the exit of a person.
The apparatus in the '560 patent makes no provision to turn lights "OFF" in a room in a shorter period of time than set by a monostable multivibrator 4e shown in FIG. 1 of the patent.
Total system operation of the '560 patent is inherently compromised in the event a door is simply left opened and not closed.
From the foregoing review of the prior art it is apparent that there are many approaches to detecting persons or objects in a zone or area of view as well as optical lenses to focus infrared energy. Some of the patents even note the need to maintain the lights to an area turned on for a period of time in the zone or area after the person is no longer detected or has departed the zone or area.
Herein reside the source of a major problem now facing a segment of lighting control industry that urges the use of automatic motion sensing to turn lights "ON" and "OFF" in a room, area or zone. Typically these motion control light switches include logic circuitry that is designed to maintain the light "ON" for a period of time e.g. 10 to 20 minutes after any bodily motion is detected. This ensures that the light remains "ON" until there is some further physical activity, which activity again triggers a 10 to 20 minute "ON" cycle.
A major disadvantage of this arrangement resides in the fact that during building occupancy hours a momentary visitor from time-to-time steps into an unoccupied room to pick up an item or drop off mail which triggers the light to turn "ON". Even though the momentary visitor leaves the room almost instantly the light remains on for another 20 minutes, much to the annoyance of an energy savings minded owner occupant that has installed the motion sensing light control switch to save electricity. One way to reduce the lighting electrical costs brought about by momentary visitors is to reduce the length of time a light remains "ON" following motion detection of a room occupant. However, the shorter the time period the greater the likelihood the room occupant motion will not be detected because they have become engrossed in their work and are remaining motionless. When the lights in the room turn "OFF" shortly after they have begun to concentrate on their work, the concentration is interrupted by the room occupant needing to wave an arm to cause the motion detecting light switch to turn the lights back "ON". Many room occupants find this arm waving activity maddening. As a consequence of this just described annoying characteristic of the lights turning "OFF" too quickly the room occupants, when possible, set the time period for the lights to be on for as long as possible thereby defeating in part the building owners efforts to save electricity due to momentary visitors.
Business and industry go through cycles of belief with respect to worker productivity as such productivity is related to private fully enclosed office space and wide open office areas partitioned off into smaller work areas. These cycles on the one hand create many private offices, each with a potential to experience unneeded lights "ON" due to momentary visitors and an off-hours phenomenon where a single employee needs to work thereby requiring all lights in a vast wide open office area to be turned "ON" when in fact only a small section of lighting in a zone the office worker is occupying is required. It is not uncommon to find an office worker departing the wide open office area and not turning off the lights because a master panel controlling all of the lights in the office area is not convenient to the worker on the way out.
The invention to be described hereinafter completely obviates the problems defined earlier which problems are not addressed by the prior art described herein before.